CHARACTERS OF TURBELLARIA 



213 



The Turbellarian worms form an exceedingly interesting group ; they 

 are often beautiful, and the ciliated ectoderm and well-developed 

 muscles enable them to move with singular grace. Although the 

 bilateral symmetry and the distinction of anterior and posterior ends is 

 quite marked, the " mouth " or single opening of the food canal is often 

 near the middle of the ventral surface. The anterior region is usually 

 furnished with tactile processes. The shape of the body in the aquatic 



Fig. 115. — Diagram of Turbellarian. — After Lang. 



C, Cerebral ganglia ; E., eye ; T., tentacle ; PH., pharynx ; Mo., mouth ; 

 M., male aperture ; P., female aperture ; the ovaries and testes are 

 branched organs on both sides, represented b^ dots. 



forms is flattened and leaf-like, as in the delicate Leptoplana, the 

 " living film " found on the shore-rocks. Fresh-water forms are 

 usually small and often minute, but those living in the sea may attain 

 a length of six inches, though most are small. Land Planarians are 

 elongated and more worm-like in shape ; they may measure a foot or 

 more in length, and are most abundant in tropi-zal countries. Some, 

 like Planaria, have so much regenerative capacity that half a dozen or 

 more may be produced by cutting one into pieces. 



